Field of the Invention
This invention relates generally to a spacer for holding a pair of disc-shaped bases of an optical disc of the air-sandwich type in spaced relation to each other, and more particularly to a spacer holder arrangement removably holding such a spacer.
Generally, an optical disc of the air-sandwich type comprises a pair of disc-shaped bases or substrates and a pair of inner and outer ring-shaped spacer elements interposed between and adhesively bonded to the pair of bases to hold them in spaced relation to each other an annular space is formed defined by the pair of bases and the inner and outer spacer elements.
The bonding between the bases of the optical disc and the spacer elements heretofore has been made using an adhesive, for example, of the ultraviolet curing type or the thermosetting type. In this method, the adhesive is applied to the spacer elements immediately before assembling the optical disc, and therefore the spacer elements are liable to be displaced out of position relative to the disc bases. For this reason, it has been necessary to keep the assembled optical disc standstill under a constant pressure until the coated adhesive is cured or set. In this respect, this conventional method is not suited for mass production.
To overcome the problem of keeping such a standstill condition, it has been proposed to use inner and outer spacer elements each having preformed adhesive layers provided respectively on opposite sides thereof. A protective film is attached to the outer side of each adhesive layer. This method overcomes the difficulty encountered with the first-mentioned conventional technique in which the adhesive is used, but it has been found to be still not suited for mass production because each spacer element has to be positioned carefully relative to the bases of the optical disc when adhesively bonding them together after removal of the protective film.